The present invention relates to a system for the non-destructive testing of the internal structure of objects. It more particularly applies to the testing of e.g. metallic objects, in cases where their internal structure has a particularly important function. It can also apply to the testing of the internal structure of potted parts.
It is known to carry out the non-destructive testing of the structure of an object, such as a metal part by ultrasonics. Thus, it is often necessary to know the internal structure of certain parts in order to better characterize them for working or shaping purposes. In the case of inspection or testing by ultrasonics, an ultrasonic beam is directed onto the object or part to be tested and the variations of the energy of the ultrasonic beam reflected on the internal defects of the object are studied in order to be able to characterize and locate these defects. In ultrasonic testing, it is very difficult to obtain a precise image of the internal structure of an object, due to parasitic echoes or clutter, which appear when the ultrasonic beams are reflected within the object. For studying the human body, it is also possible to use X-ray tomography. According to this process, an image of the section of the human body or one of its organs is reconstituted by treating information relative to the attenuation of an X-ray beam which has traversed the body or organ. The attenuated X-ray beam is collected or trapped by one or more detectors, which make it possible to measure this attenuation and deduce from it the densities of the traversed tissues. Whereas conventional radiographs reveal cumulative radiation attenuations, the sectional image frees the tissues observed from the accumulation of shadows of the surrounding organs. The resolution level obtained makes it possible to detect limited variations in the density of tissues and consequenty improve the differentiation between two adjacent tissues.
In general, X-ray tomographs comprise a mechanical assembly, which is able to rotate and whose axis essentially passes through the centre of the part of the body or organ examined. This assembly supports an X-ray generator and a radiation detector, which can themselves move in a linear manner in a plane perpendicular to the axis of the system. The generator and the detector comprise diaphragms making it possible to define observation sections of limited thickness in the body or organ. The analog signals of the detector are converted into digital pulses and are then processed by a computer making it possible to control circular and linear displacements, acquire measurement data, reconstitute and display on a screen the reconstructed image and store the reconstructed image elements in a store. In general, this computer is associated with complementary peripheral units, such as a printer making it possible to obtain information on the tissues traversed by the X-rays. The X-ray generators used in human body tomographs have a voltage not exceeding 150 V, due to the limited density of the tissues studied. Thus, the photon-material interaction phenomena results solely from the photoelectric absorption of the diffusion of the X-rays, whose combination leads to an exponential attenuation thereof.
In order to carry out faster tomographic examinations and so as not to expose the human body to X-rays for excessively long periods, whilst improving the quality of the sectional images obtained, the existing tomographs have a large number of detectors, so that the X-ray beam from the generator is shaped like a fan extending from the generator to the detectors. Thus, with such tomographs, it is no longer necessary to linearly displace the generator-detector assembly to obtain the image of a complete section of the human body.